Method and apparatus for correcting optical spot position

Abstract

A method and apparatus for producing a set of compensated commands for a spot position mechanism. A dimensioned grating is placed across the beam path and an image of the grating is generated. The image is analyzed and the pixel position of the grating edges is compiled. From this a list of grating edge distances is produced and used to generate observed edge positions. A line is fit and removed from the list to produce a list of observed errors. The observed errors are correlated to the proper position space and a set of positions errors is produced. The position errors are subtracted from the command positions to produce a set of correction positions. This set of corrected positions can be used to command the spot position mechanism. The positions might also be tabulated and referenced. Interpolation between the points can also be performed.

What is claimed is: 
     
       1. A method for generating at least one command which compensates for systematic errors in a spot positioning device having a scanning beam and scanning surface, the steps comprising: (a) positioning a dimensioned grating with grating edges on the scanning surface;   (b) generating scan pixel data corresponding to the beam path;   (c) finding the pixel position of grating edges;   (d) using the pixel positions to generate observed edge positions;   (e) using the observed edge positions to produce a list of observed errors; and   (f) generating a set of compensated commands from the list of observed errors; wherein step (d) further comprises: multiplying the pixel positions by the size of the scan pixel to produce a list of grating edge distances; and   generating observed edge positions from the list of grating edge distances.     
     
     
       2. The method of claim 1, wherein the steps are reiterated to refine the set of compensated commands. 
     
     
       3. The method of claim 1, wherein after step (f) an additional step comprises: (g) tabulating and storing the list of compensated commands.   
     
     
       4. The method of claim 3, wherein after step (g) an additional step comprises: (h) interpolating between tabulated points.   
     
     
       5. A method for generating at least one command which compensates for systematic errors in a spot positioning device having a scanning beam and scanning surface, the steps comprising: (a) positioning a dimensioned grating with grating edges on the scanning surface;   (b) generating scan pixel data corresponding to the beam path;   (c) finding the pixel position of grating edges;   (d) using the pixel positions to generate observed edge positions;   (e) using the observed edge positions to produce a list of observed errors; and   (f) generating a set of compensated commands from the list of observed errors;   wherein step (b) further comprises: scanning the beam path over the grating a plurality of times to generate scan pixel data; and   averaging the plurality of scans to generate averaged scan pixel data corresponding to the beam path.     
     
     
       6. A method for generating at least one command which compensates for systematic errors in a spot positioning device having a scanning beam and scanning surface, the steps comprising: (a) positioning a dimensioned grating with grating edges on the scanning surface;   (b) generating scan pixel data corresponding to the beam path;   (c) finding the pixel position of grating edges;   (d) using the pixel positions to generate observed edge positions;   (e) using the observed edge positions to produce a list of observed errors; and   (f) generating a set of compensated commands from the list of observed errors;   wherein step (c) further comprises: examining the scan pixel data starting at the middle of the data and working outward to detect grating edges to produce a list of pixel positions of the grating edges.     
     
     
       7. The method of claim 1, wherein step (e) further comprises: fitting a line to the observed edge positions; and   removing the line from the observed edge position data to produce a list of observed errors.   
     
     
       8. The method of claim 1, wherein step (f) further comprises: correlating the list of observed errors to the position space of the spot positioning device to produce a set of position errors;   subtracting the position error corresponding to a desired command position to produce a compensated command for the spot positioning device.   
     
     
       9. The method of claim 1, wherein step (e) further comprises: fitting and removing a line from the observed edge positions to produce a list of observed errors; and   performing a smoothing operation on the list of observed errors.   
     
     
       10. The method of claim 9, wherein the smoothing operation includes a low pass filter. 
     
     
       11. A method for generating a set of compensated commands which correct for systematic errors in a spot positioning device having a scanning beam and scanning surface, the steps comprising: positioning a dimensioned grating with grating edges on the scanning surface;   scanning the beam path over the grating a plurality of times to generate scan pixel data;   averaging the multiple scans to generate averaged scan pixel data corresponding to the beam path;   finding the pixel position of grating edges to produce a list of pixel positions of the grating edges;   multiplying the pixel positions by the size of the scan pixel to produce a list of grating edge distances;   generating observed edge positions from the list of grating edge distances;   fitting a line to the observed edge positions;   removing the line from the observed edge position data to produce a list of observed errors;   correlating the list to the position space of the spot positioning device to produce a set of position errors;   subtracting the position error corresponding to a desired command position to produce a set of compensated commands.   
     
     
       12. The method of claim 11, wherein an additional step is added after the last, comprising: tabulating and storing the set of compensated commands.   
     
     
       13. The method of claim 12, wherein an additional step is added, comprising: interpolating between the tabulated commands. 
     
     
       14. An apparatus for generating a set of compensated commands which correct for systematic errors in a spot positioning device having a scanning beam and scanning surface, the apparatus comprising: a beam generator,   a spot positioning device which steers the generated beam across a beam path;   a dimensioned grating device positioned in the beam path and producing a grating edge signal;   a sensing device which receives the grating edge signals;   a position command processor which takes the grating edge signals and generates compensated commands for the spot positioning device:   wherein the position command processor performs the following steps: (a) finding the pixel position of each grating edge;   (b) using the pixel positions to generate observed edge positions;   (c) using the observed edge positions to produce a list of observed errors; and   (d) generating a set of compensated commands from the list of observed errors wherein step (b) further comprises: multiplying the pixel positions by the size of the scan pixel to produce a list of grating edge distances; and   generating observed edge positions from the list of grating edge distances.       
     
     
       15. The method of claim 1, wherein the position command processor reiterates the steps to refine the set of compensated commands.